This invention relates to a solar panel of the type which particularly but not exclusively may be utilised for the heating of water for domestic or industrial purposes.
Solar panels which collect and utilise the energy present in solar radiation are well known. A typical known construction of solar panel comprises an array of cylindrical cross section relatively thick-walled pipes in thermal contact with a plate of heat conducting material which is coated with a radiation absorbing medium. Solar radiation incident upon such a plate is absorbed thereby resulting in an increase in its temperature and of the pipes in contact therewith. Water or other fluid flowing through the pipes is thereby heated and may be utilised either directly or indirectly for a variety of purposes.
It is known to improve the efficiency of such a solar panel by reducing the transfer back to the environment of absorbed heat energy by providing one or more cover plates over the absorber plate. Such a cover plate may be constructed of a material which is characerised by having a high transmission factor for incident solar radiation and a low transmission factor for heat radiated from the absorber plate.
It is also known to reduce the emission of heat radiation from such an absorber plate of a solar panel by the application to its surface of a selective coating which exhibits high absorption for radiation having a short wavelength typically of less than some 3 microns and which exhibits relatively low emission for radiation having longer wavelengths. Furthermore, it is well known that efficiency can be improved by reducing or eliminating heat losses from the rear and side surfaces of such solar panels by the provision of thermal insulation of conventional form.
A typical solar panel of the type known in the prior art is illustrated in FIG. 1 of the accompanying drawings. Typical dimensions for such a solar panel in which the pipes and the absorber plate are formed from copper may be as follows:
______________________________________ internal diameter of pipe 10.0 mm wall thickness of pipe 1.2 mm spacing between centre axes of adjacent pipes 150.0 mm thickness of absorber plate 0.5 mm ______________________________________
Such known solar panels as described above can suffer from a number of disadvantages. One such disadvantage is that the cost of the absorber plate is relatively high particularly when such a plate is coated with a radiation absorbing medium. A further disadvantage is that the heat exchange surface in contact with the fluid flowing through the pipes is relatively small in comparison with the total absorbing surface of the absorber plate. For example, a section of solar panel having a total absorbing area of 30,000 cm.sup.2 may only have a total heat exchange surface in contact with the fluid of 5,662 cm.sup.2. A still further disadvantage is that the relatively high mass of the metal pipes and of the absorber plate results in the solar panel being of significant weight which can adversely influence the ease of installation of the panel and its location. Such a relatively high mass also represents an undesirable thermal dead load which leads to an extended warm-up time of the solar panel. By way of example, a section of panel having a total absorbing area of 30,000 cm.sup.2 as mentioned above may contain approximately 20 kg of copper in the pipes and associated absorber plate.
it is an object of the present invention to provide a new and improved solar panel which will overcome certain of the disadvantages associated with known solar panels.